Cave creatures live buried alive. Troglobites—the technical name for these millipedes, spiders, worms, blind salamanders, and eyeless fish—are made to navigate, mate, and kill amid perpetual darkness, desperate starvation, poison gases, and endless labyrinths of stone. Evolved in isolation and unable to disperse, species often consist of just a handful of individuals in one cave, or one room of one cave. Their existence raises many questions. How did they get there, and when? How do they survive—and how much longer can they hang on? Increasingly, many are threatened by pollution, quarrying, and vandalism. Ultimately, they are connected to a surface ever more populated, and penetrated, by us. They are the wildest canaries in the coal mine.

Worldwide, perhaps 90 percent of caves lack visible entrances and remain undiscovered. Even in well-explored caves, troglobites are expert at hiding. The roughly 7,700 species known are probably only a small taste of what lives below.

To survive stagnant, low-oxygen air in dead-end recesses and months without food, many troglobites have super-slow metabolisms. And because they live slow, they live long. The Orconectes australis crayfish of Shelta Cave in Alabama may reproduce at 100 years, and live to 175. Many troglobites possess extraordinarily long legs (and lots of them) with spiky feet adapted for getting over rocky terrain and sticking to moist surfaces. Pigments (which protect surface organisms from ultraviolet rays) and eyes disappear; for some creatures, eyeless sockets serve as fat reservoirs. Instead of vision, many have elaborate appendages and beefed-up nerve centers to interpret slight air-pressure or temperature changes, sounds, and smells. This sensory equipment lets them travel, sense objects moving or still, ambush prey, and, according to a recent study of troglobitic fish, judge the size and suitability of prospective mates, sight unseen.

Cave biology might be dated from 1797, when foot-long Proteus salamanders were first seen in Slovenian caves. They were the first, and still among the largest, known troglobites; locals at first thought they were baby dragons. Since then, scores of blind salamander and fish species have turned up in places like Texas’ vast Edwards aquifer, where they sometimes shoot up in artesian wells tapping unseen watery caverns below.

Startling new discoveries are now coming out of Sequoia and Kings Canyon National Parks, in the Sierra Nevada mountains of California. Here, scientists recently announced the discovery of some 30 new invertebrate species—an extraordinary number for such a small area—all still undescribed and unnamed. Scientists are also finding new caves—255 at last count, a number that increases every few months.